Photosynthetic responses of tomato leaves to salt and cadmium stresses: Growth and chlorophyll a fluorescence kinetic analyses

Abstract

This study investigated the effects of salinity (NaCl) and cadmium (Cd) on leaf growth and photosynthetic parameters of tomato plants (Solanum lycopersicum cv. Rio Grande). Cd and NaCl treatments considerably reduced leaf dry matter and leaf area of tomato plants. Stomatal conductance decreased significantly with increased NaCl and Cd in the growth medium, with the decrease occurring at an early stage under Cd treatments. For the fluorescence parameters, there was no significant difference in the maximum quantum efficiency of PSII (Fv/Fm) for either type of stress. However, the quantum yield of PSII photochemistry (ΦPSII), photochemical quenching (qp), and the intrinsic efficiency of PSII (Фexc) decreased significantly under both NaCl and Cd treatments. Decreases in ΦPSII, qp, and Фexc were coupled with a significant increase in non-photochemical quenching (NPQ), and the highest NPQ was obtained in NaCl-treated plants. The correlation between electron transport rate (ETR) and stomatal conductance showed that stomatal closure is associated with a down-regulation of ETR, which is compensated by an increase in non-photochemical quenching.